There are many types of solid deodorant and antiperspirant sticks that are commercially available or otherwise known in the art. These solid sticks are designed to provide effective perspiration and odor control while also being cosmetically acceptable during and after application onto the underarm area of the skin, and are typically packaged in dispensing containers suitable for conventional application of the composition to the skin by a consumer. In this context, “cosmetically acceptable” means that the product glides on smoothly during application, is non-irritating, and results in little or no visible residue (e.g., low residue performance) after application to the skin.
The conventional way of making such solid deodorants and antiperspirants includes combining all ingredients in a heated hold tank. The ingredients are thoroughly mixed and heated to several degrees above the complete melt point of the mixture. Once the ingredients in the heated tank are completely melted and mixed, a small feed stream is pumped through a scraped surface heat exchanger to initiate crystallization. The feed stream then goes through a filler where it is fed into canisters. Some portion of the feed stream can be re-circulated through a second heat exchanger to melt the crystals before being deposited back into the heated hold tank. This process is continued until the hold tank is emptied and a new batch is started. There are several limitations associated with a conventional process described above.
First, the quality of the crystal structure is limited by the process since only a small portion of the process stream is exposed through indirect contact to the cooling media to result in spontaneous nucleation. In a scraped surface heat exchanger the portion of the stream exposed to the chilled surface is increased by the scraping action of the blades to renew and clear the surface for indirect contact. However, the freshly nucleated product that is scraped from the wall is re-introduced into the hot bulk product flow. Near the inlet of the scraped surface heat exchanger the bulk product flow is above the melting point of the just nucleated crystals, so the thermal driving force is for re-melting the just formed crystals. By the exit of the scraped surface heat exchanger the bulk product flow is typically at a temperature below the melting point of the crystalline material, but above it's spontaneous nucleation temperature—this is known in the art as the Metastable Growth Region. In this temperature region, crystalline material can grow on existing crystals, but generally are thermodynamically unable to form new, independent crystals. Accordingly, much of the crystallization occurs in the Metastable Growth Region and results in relatively large, non-uniform crystals that are less than optimal in their ability to harden a solid stick suspension, and resist weeping in soft solid compositions.
Therefore, it would be desirable to create a process that would result in a substantially higher proportion of the stream being crystallized in the spontaneous nucleation region to create a crystal structure with smaller, more uniform crystals that could harden a solid suspension using less total gellant and result in soft solid suspensions that can better resist weeping.
Another disadvantage of the conventional method includes the possibility for heat sensitive ingredients to deteriorate during the period of time required to formulate and completely process a batch at the elevated holding temperatures. Therefore, it would be desirable to create a processing method that would shorten or even eliminate the time period required for the heat sensitive ingredients to be held at elevated temperatures.
Also, the conventional process itself is relatively complex and requires capital equipment with moving parts that can be expensive and require periodic maintenance to keep it in good operating condition. Accordingly, it would be desirable to create a process with no moving parts to reduce capital, maintenance and operating costs.
U.S. Pat. No. 6,338,840 describes a process and an apparatus for forming deodorant or antiperspirant sticks by forming a mobile composition for dispensing into containers or molds under pressure, preferably using a screw extruder, particularly a twin-screw extruder. The process claims the benefit of allowing incorporation of sensitive ingredients and ameliorating sedimentation of particulates. However, this process also appears to have at least some of the same limitations as the above-described conventional process in that only a small portion of the process stream is exposed through indirect contact to the surface of the cooling media. Additionally, the extruder has multiple moving parts that are expensive to maintain.
WO 02/053109 describes a process for preparing a solid free-standing cosmetic composition, whereby the composition is pumped through a cooled pipe without being subjected to mixing during its passage through the pipe. While this process does not employ a forced extrusion, it still requires external cooling means, such as a cooling jacket surrounding the pipe, to nucleate and crystallize the crystal matrix with all the aforementioned limitations.
The present invention comprises a novel and advantageously simple process for making solid cosmetic compositions, such as, for example, deodorant and antiperspirant sticks, while avoiding the limitations of the prior art.